前端面试之js篇（一）

//js有6种数据类型（5种基本数据类型、1种复杂数据类型）
	1.String字符串; 2.Number数字; 3.Boolean布尔; 4.Null空对象指针; 5.Undefined没有定义
	6.Object对象; 
	7.Function函数; 8.Array数组;
//isString(str)
	① typeof 'str' === "string"
	② Object.prototype.toString.call('str') === "[object String]"
	③ String('str') === 'str'
//isNumber(num)
	方法一：!isNaN(parseFloat(1)) && isFinite(1)
	方法二：typeof 1 === "number" && !isNaN(1)
	方法三：typeof 1 === "number" && isFinite(1)
	方法四：Object.prototype.toString.call(1) === "[object Number]"
	方法五：1 === +1
//isBoolean(b)
	① Object.prototype.toString.call(true) === "[object Boolean]"
	② typeof false === "boolean"
//isNull(null)
	① Object.prototype.toString.call(null) === "[object Null]"
	② typeof null === "object"
//isUndefined()
	① Object.prototype.toString.call() === "[object Undefined]"
	② typeof a === "undefiend"
//isObject(obj)
	① Object.prototype.toString.call({}) === "[object Object]"
	② typeof {} === "object"
//isFunction(func)
 	① Object.prototype.toString.call(function(){}) === "[object Function]"
 	② typeof funciton(){} === "function"
 	//js固有函数
 	③ Object.prototype.toString.call(clear) === "[object Function]"
 	③ typeof clear === ”function“
//isArray(arr)
	① Object.prototype.toString.call([]) === "[object Array]"
	② typeof [] === "object"

setInterval(function(){
	var time = new Date(),
		yyyy = time.getFullYear(),
		M = time.getMonth()+1,
		d = time.getDate(),
		h = time.getHours(),
		m = time.getMinutes(),
		s = time.getSeconds(),
		MM = M<10?('0'+M):M,
		dd = d<10?('0'+d):d,
		hh = h<10?('0'+h):h,
		mm = m<10?('0'+m):m,
		ss = s<10?('0'+s):s;
	var now = yyyy+'-'+MM+'-'+dd+' '+hh+':'+mm+':'+ss;
	console.log(now);
},1000)
//ES6

//js
document.getElementById("text").style.display="none"
//jQuery
$('.a').hide(1000); $('.a').show(5000); $('.a').toggle(1000)
$('.a').addClass('hide'); $('.a').removeClass('hide'); $('.a').toggleClass('hide')
//vue
<div v-if="a">demo1</div>
<div v-if="{hide:a}">demo2</div>
data层改变a的布尔值

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<div id="field">
	<input type="text" value="user name">			
</div>
<span class="red"></span>

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